Ammunition feed belt linkage bracket

The invention described was made in the performance of official duties by one or more employees of the Department of the Navy, and thus, the invention herein may be manufactured, used or licensed by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The invention relates generally to ammunition feed linkages. In particular, the invention relates to spacer tabs that separate ammunition rounds from their guided feed system while mitigating electromagnetic hazards.

The United States Navy employs guns for firing 20 mm ammunition. Such guns include the M61 Vulcan cannon for Phalanx and M197 gatling gun. Modern militaries employ such guns fed by cartridge belts, which are pulled by the gun's feed mechanism. A cartridge chain concatenates ammunition rounds to form the belt of bullets fired from the guns.

Solid-state radar systems are significantly increasing the Navy shipboard operational electromagnetic environment (EME) onboard numerous Naval platforms. Legacy ordnance systems are being evaluated to the increased EMEs to ensure that ordnance are not inadvertently duded or initiated, specifically through Hazards of Electromagnetic Radiation to Ordnance (HERO) testing.

Electrically primed 20 mm ammunition has been evaluated for HERO and determined to be HERO susceptible to EMEs in multiple frequency bands when platform loaded on aircraft. Hence, safety for personnel and equipment necessitates HERO Emissions Control (EMCON) for specific Naval transmitter systems (i.e., reduced power, sectoring, etc.) during aircraft departure and recovery. Such restrictions have significant potential to affect ship performance and compromise her crew's mission.

Aircraft gun configurations include an ordnance container (or drum), a feed chute which carries the ammunition from the drum to the gun, a feeder system to pull the rounds through the chute and the gun. Un-commanded 20 mm round initiation has occurred during a HERO test. Investigation and analysis revealed causation by capacitive coupling between metal tabs on the aft of feed chute to the 20 mm electric primer.

At frequencies in X-Band, the metal tab of the radiation hazard (RADHAZ) link and/or the feed chute act as a patch antenna with resonant frequency determined by the distance between the tab and the 20 mm primer. Similarly in S-Band, the chute assembly itself acts as a receive antenna capacitively coupling sufficient energy to inadvertently initiate the 20 mm primer.

This effect has been verified both experimentally and through modeling and simulation (M&S) with consistent results. The most cost effective option to mitigate HERO was determined to be through modification of the 20 mm feed chute, because these items have the most limited service life and have to be replaced often.

Conventional ammunition linkages yield disadvantages addressed by various exemplary embodiments of the present invention. In particular, exemplary embodiments provide a guidance tab for separating a cartridge round at its base from an aft linkage bracket within an ammunition chain. The tab includes a plate, a pair of legs and a pair of feet, and is composed of polyamide-imide. The plate has an obverse surface for engaging the base of the cartridge round and a reverse surface for engaging the aft linkage bracket. The plate is oriented along a longitudinal direction of the ammunition train and a lateral direction orthogonal to an axial direction of the cartridge round. The pair of legs extend from flanking sides of the plate in the axial direction towards the aft linkage bracket. The pair of feet extends substantially parallel to the plate. Each foot extends from a respective leg of the pair of legs.

In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

The disclosure generally employs quantity units with the following abbreviations: length in meters (m) or inches (″), mass in grams (g), time in seconds(s), angles in degrees (°), force in newtons (N), temperature in kelvins (K) or degrees fahrenheit (° F.), energy in joules (J), potential in volts (V), electric current in amperes (A) and frequencies in hertz (Hz).

The purpose of this design is to mitigate a Hazards of Electromagnetic Radiation to Ordnance (HERO) issue for aircraft utilizing 20 mm gun systems. Feed chutes load ammunition belts to the guns for firing rounds contained therein. Both modeling and simulation (M&S) and laboratory testing reveal that 20 mm ammunition can be inadvertently initiated when exposed to emerging EMEs. The exemplary 20 mm feed chute component design mitigates this vulnerability by selecting appropriate materials and designing a new cartridge guide shape, while nonetheless satisfying all structural, reliability and environmental requirements for the feed chute.

Ammunition must be stowed in an orderly fashion to maximize the number of rounds that available to a gun. Storage and delivery of the rounds can be adequately accomplished by an ammunition handling system (AHS). The gun must be steerable so as to be able to point towards targets. This imposes variability of the gun's orientation relative to the AHS.

A feed chute connects the AHS to the gun, and offers adequate flexibility to enable continuous transfer of ammunition between them. This transfer occurs along a belt path suitable for articulation of the retention links used between each concatenated ammunition round in the belt.

Feed chutes must be able to flex in a variety of directions, often concurrently along multiple compound angles while traveling along the feed chute's path. The feed chute must be able to swiftly and repeatedly reposition into new orientations as the gun system rapidly maneuvers during operations to effectively engage targets in a timely manner. This must be accomplished without binding up the continuous delivery of the ammunition rounds.

Feed chutes must be able to function properly in various severe operational conditions, often concurrently. Therefore, any alteration to an already fielded feed chute must be compatible with these same conditions. To preclude reduction in operation capabilities, high level requirements were developed to measure them against for suitability. These requirements were:

presents an example in a perspective viewwith a compass roseof a partial ammunition feed chute for loading 20 mm cartridge case assemblies(also called “rounds”) within cartridge case subassembliesthat concatenate as an ammunition chain or belt and slide along rails. The compass roseprovides Cartesian coordinates in the belt longitudinal X, lateral port Y and cartridge axial Z directions. Ammunition travels along the X direction, while the Z direction in relation to the gun (not shown) points from breech to muzzle for reference. Artisans of ordinary skill will recognize that 20 mm ammunition is merely exemplary and not limiting, although primary analysis and design has emphasized the 20 mm configuration.

Upper (i.e., towards the gun's muzzle) linkagesinclude hoops (over the cartridge tips) that connect to proximal flanges held by corresponding proximal clamps. Lower (i.e., towards the gun's breech) linkagesinclude retention bracketsheld by distal clamps. Bottom guidesseparate the roundsfrom the bracketswhile riding along the linkagesand. The bottom guidesconstitute spacer tabs to ensure separation between roundsand the brackets.

Additional sets of transverse guides include lower transverse, mezzanine, upper transverseand intermediate. These guides,,,andare typically composed of stainless steel for durability. Such guides engage the linkagesandto enable the case subassemblyto translate with the roundthrough the feed chute. The lower and upper transverse guidesandinhibit lateral wobble by the round.

show isometric viewsof the cartridge case subassemblytowards the breech end with corresponding compass roses.presents the perspective from offset the muzzle, whileillustrates observation from offset the breech. The aft baseof the roundrests on the bottom guide, which rides on the bracket. Railspassing between the transverse guidesandand the linkagesandprovide continuity between subassemblies. The bracketsecures the guidevia a pair of rivets, each of which pass through aligned corresponding through-holes.

The exemplary bracketand bottom guideas components to the lower linkagesare modified from the conventional by modest alterations in geometry, as well as substitution of composition material from an electrically conductive metal to a rigid polymer. Under HERO, the conventional bottom guide permits inadvertent initiation of the primer in the cartridge round. Replacing electrically conductive stainless steel with a dielectric insulator as exemplary bracketand bottom guidebecomes necessary due to higher electromagnetic energy from radar upgrades that threaten HERO reaction.

Such substitution for the bracketand guidethat the baseof the roundrides against while traveling through the ammunition chute requires a material that would mechanically behave similarly to steel in operational conditions. A search for the material that satisfies the requirements identified polyamide-imide (PAI) as a candidate. PAI constitutes an amorphous polymer that possesses appropriate properties, such as high strength and melt processibility, heat tolerance and chemical resistance.

Solvay Specialty Polymers under tradename Torlon® represents a prominent distributor of PAI materials. Various types of Torlon® are available, and properties vary per type. To replace stainless steel for the bottom guide, injection molded Torlon® 5030 plastic was selected. PAI material properties can be read at https://www.professionalplastics.com/professionalplastics/content/Torlon5030datasheetPAI.pdf for reference. Note that Torlon® 5030 includes 30% glass-fiber reinforcement, with thermal expansion similar to aluminum.

Initial calculations for use of injection molded Torlon® 5030 show that when the component is made thicker, the exemplary guideprovides:

show isometric assembly viewsof bracket components for the lower linkages, including a compass rosefor orientation. The bottom guideand the transverse guideare shown mounted to the bracketof the lower linkage. The railspass through gapsbetween the guidesand the bracket. In, the guidesand rivetsare omitted for clarity, displaying through-holesin the guide.

shows an isometric exploded viewof bracket components with the guidelevitated above the bracket, showing through-holesin the bracket, which includes a base spanwith flat indentionsfor receiving the guide, and include the holes. Port and starboard armsandflank the spanfor attaching their respective lateral guides. Indentson the armsandprovide the gapsthat enable passage of the rails.

show elevation cross-section viewsof the cartridge case subassemblytowards the breech end, along with a compass rosefor orientation, with the former illustrating components from, while the latter presents a detail region. In particular, the reformed geometry outlinefor the exemplary bracketcan be compared to the conventional geometry outlinefor that component's predecessor that employs a stainless steel conventional bottom guide. A vertical gapcompensates for the increased thickness of the reformed PAI guideas compared to that component's conventional stainless steel version.

Design efforts have been conducted that enable incorporating the thicker component made from PAI, while maintaining required dimensional control of inside surfaces of feed chute assembly. Redesign of the bracketthat the bottom guidemounts to has also been accomplished. This presumably enables present feed chute vendor to continue using currently operable fabrication tools, while enabling insertion of the new design for future production at a preferred time, with minimal changes. This was accomplished by using the same length and type of rivetscurrently in operation.

shows isometric viewsof the bottom guide. The left illustration shows the guidefrom offset the muzzle, while the right illustration shows the guidefrom offset the breech, both clarified by respective compass roses. In the configuration presented, the bottom guideconstitutes a unitary component with a platehaving a fore nosetowards the feed chute and an aft tailtowards the stowage magazine (not shown).

A pair of flanking legsextend axially adjacent the tail, and a pair of feetextend outwardly from the legs. Each footincludes a through-holecorresponding to the holeat the baseof the bracketto receive the rivet. The plateincludes an obverse surfacethat supports the round, and a reverse surfacethat faces the bracket.

The plateis oriented along a longitudinal direction (X) of the ammunition train and a lateral direction (Y) orthogonal to an axial direction (Z) of the cartridge round. The pair of legsextends from flanking sides of the platein the axial direction (Z) towards the aft linkage bracket. The pair of feetextends substantially parallel to the plateoutward from the plate. The exemplary bracketdoes not actually bend, but extends to provide relief by lowering the mounting surface for the exemplary guidethat has been thickened to accommodate its material substitution.

shows an elevation cross-sectional viewof the bottom guidefeaturing dimensional alterations as a consequence of material substitution of PAI from stainless steel. In particular, the thicknessand slope angleof the plateincrease from 0.025″ and 2.0° for steel to 0.065 “and 4.46° for PAI. In addition, the heightof the legsincreases from 0.0772” for steel to 0.1292″ for PAI. Stainless steel has a density of 7.93 g/cm, compared to Torlon® 5030 of 1.61 g/cm, which is about one-quarter that of steel.

The PAI component for the bottom guidehas greater thicknessthan the original stainless steel counterpart. This provides sufficient material to ensure that the guideprovides the same dynamic response to loads as the original design. Because of this, the redesigned feed chute assembly is expected to operate functionally the same as currently.

Changes in thicknessof the guidedue to additional material required the part to have a higher clearance from its bracketthan conventionally. This change was designed to provide the same clearance between the replacement PAI component and its bracketas originally existed with the conventional steel component. This ensures the feed chute maintains its mobility in the different directions that already exist. The angleof the slope of the guideincreases slightly, providing the same clearance between itself and the bracketforward as previously existed.

The exemplary guideproduced from PAI enables the chute to contort into the same positions as before, while using a lower percentage of its deflection capabilities than when previously composed from stainless steel. This increases the life cycle of the guidewithout significantly increasing the replacement rate of feed chutes, if at all.

The exemplary guidecomposed of PAI is not electrically conductive, which inhibits antenna behavior. This prevents initiation of a roundwhile in the feed chute due to HERO. Should additional testing suggest other components in nearby proximity cause issues, they too can be made from Torlon® PAI. Because the bracketis already being modified, incorporating these both components fabricated from PAI would entail the same overall geometry and capability as conventionally, but with greatly improved HERO resistance. Existing feed chutes expect to be remanufactured to the exemplary HERO-safe design by removing the previous guides and brackets and replacing with the PAI substitutes.

Mitigation options for this HERO issue were investigated and determined to fall in three categories: (1) replacement of 20 mm electrically primed guns and ammunition with percussion primed guns and ammunition for all aircraft configurations, (2) increase the shielding effectiveness (SE) of the aircraft around the feed chute and gun assemblies to reduce the incident EME on the ammunition, and (3) to redesign the chute to act as a less efficient antenna or mitigate the radio frequency (RF) coupling path to the 20 mm primer.

Navy leadership determined that the first option of replacing all legacy electrically primed guns and ammunition with percussion primed is extremely costly and would significant impact the Navy's current inventory of 20 mm ammunition. Additionally, current Navy aircraft employing 20 mm gun configurations have been in the fleet for many years, and modification of the aircraft for the second option to increase SE around the gun would adversely affect aerodynamics, weight, center of mass, etc. and hence rejected as not being a cost effective option. The most cost effective third option to mitigate the HERO issue was determined to be through modification of the 20 mm feed chute, because these items have the shortest service life and must be replaced often.

The United States Department of Defense (DoD), as well as other foreign counties use 20 mm gun systems on aircraft which are exposed to significant EMEs on ships or land based facilities. The material change and modified 20 mm feed chute design has a significant number of use cases for various aircraft systems which may be affected by emerging transmitter systems leveraging solid-state technology. There are also ground and sea-based applications of HERO-susceptible systems that would benefit from this solution. As alternative approaches to mitigate this HERO threat have significantly more costs, there will likely be significant interest in this design.

While certain features of the embodiments of the invention have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments.